Etching process and composition for use therein



ETCHING PROCESS AND COMPOSITION FOR USE THEREIN Filed Sept. 8, 1930 Pea/lsf Pau/der Z'n Pr/'a/ Zes/lsf Pau/der S14/vento@ MWMMFM and; wur! PatentedApr. 1s, 1933 5 f UNITED STATES PATENT oFFlci-z Innova-r. connor, or Luzmum rms'nvmn, nssrehmn or crm-nm. 'ro LU- zrmrr :lorca conm, or Luznmm, rnsusrrvama, A coraa'rmsm' consrs'rnc or Luo n. concur, wmnnm r. concur, am: nicmar. n. coneau :creme rnocnss im lconrosrrron ron vsn 'rnmnm Application med September 8, 1980. Serial lo. `480,814r.

'.lhis invention relates to etching processes and compositions for use therein, and has for previously prepared negative inl a well its general objects the provision of an improved process of this type-as ursued in connection withv the etching or p oto-engraving of printing plates or the like,`and the provision of a new composition of matter which is em lo edthcrein.

git eordinaryphoto-engra process as 4 generally carried out, a p ate of copper or zinc commonly called a flat, is coated with Y a suitable enamel or sensitizmg solution,- such as, for example, a bichromate albumen com os1tion,the thin film thus formed is drie and the plate is then printed from a known manner. The prmting process, and the subsequent developing, as will be .readily understood, cause those portions of the-film of s'ensitizl material which are exposed to the actionlthe light to adhere strongly to the plate to form a'base for the resist material to be later a plied. The developing of the plate is us y accomplished by immersion in water.

The developedsurface of the .plate is then rolled with ink and brushed with dragons blood or othersuitble or cmnbionl emlo edito in ow er, usua y y t e so- Ea ed foipwzyg method in which the powder is brushed backward and forward in each of two directions substantially ,at right angles to each other, so as to ensure that the substantially vertical edges 'of the areas to which the ink has been applied, as well as the to surfaces thereof, shall be thoroughly coate Thel high light areas and other fplortions which are to be etched are care lly brushed preferably' with a verysoft camels hair brush, to free them from any of the powder which might have a tendency to adhere thereto.

The plate is then gently and evenly heated until'the coating of mk and topping powder is burned in or ,melted together to form an acid resistant covering for the portions of the plate which are not to be cut away during the etching process. The next step in the process comlrsitses giving the plate what is termed the blte or immersion inthe etching bath. In the Acase of a copper plate, the bath is generally an iron perchloride solutionand in the case of a zinc plate, ,with which the prsent invention is more concerned, the etching solution is usually composed-l of nitric acid. The

first bite? is also usuall made in a more dilute solution and is of a orter duration than subsequent immersions.

This irst bite has its greatest eiect on the high light areas of the plate, and -in the ordinary methods, a routing tool is sometimes employed to cut away the larger of these areas to ensure that no part of them will' make an impression upon the sheet during the printing operation in which the completed plate is finally used. A

It will be understood that the operations just described, especially'those of applying the powdered dragons blood to the plate, brushing it four ways, and the careful brushing required in removing every vestige of the powder from the bottoms or portions ofthe plate to be etched, are very tedious processes requiring theA attention of Ahighly skilled experts and consuming a relatively great amount of time. This is especially true of the last named brushing process when practiced in connection, with fine line or half tone work where' 'these areas are very minute.

After the first bite is accomplished the plate is rinsed with water and again powdered four ways to apply a coating of resist to the newly exposed' edges of the raised portions, i'n order to prevent undercutting of these edges and the consequent spoiling of the plate. `It is highly important to again brush all of the powder from the areas to be etched so as to maintain a clean bottom. The plate is again burned in and then alternately etched and powdered,-usually until it has received4 four bites,-and iinall of the resist is dissolved and washedY oil with benzol or other suitable cleanup dope and the finished plate,is ready for mounting upon 'a block for use in a press, or prepared in any other manner for impressing its en- 1glgfrkaved design upon a sheet of paper or the The method forming the sub 'ect 'matter of my invention is especially app 'cable to zinc plates which are etched in a nitric acid bath, and in the practice thereof the above described general -process is modified as will be hereinafter described in connection with the accompanying drawing, in which the figures are great y enlarged and somewhat diammatic cross sectional views of a late uring successivel stages in the etc ing process.

In said drawing:

Fi e 1 shows the plate or flat aftei` bemg deve oped, rolled with ink, and powdered before the first bite;

Figure 2 shows the plate after being burned in and given the first bite in the etchin bath;

igure 3 shows the plate with my novel composition applied thereto;

F1 e 4 shows the plate after being powdere for the second bite;

Figure 5 illustrates the plate after the burning in process rior to the second bite;

Figure 5a is a ragmentary, magnified view of the portion of the surface of the plate enclosed in the circle in Fig. `5` and showing the layers of resist and of my novel composition `as they4 appear on the bottoms of the plate, and l Figure 6 illustrates the greater de th of cut and smoother bottom attained y the use of my process and composition as compared with Figure 7 which illustrates a plate which has been treated without the use of my composition.

After performing the successive steps of sensitizing, developin rolling'V with ink,

wdering, brushing, urning in, and sub- ]ecting the late to the first bite, (certain stages of t is preliminary process bein shown in Figs. 1 and 2), the plate is rins with water and then flowed with a solution which, for obtaining the best results, is composed of the following ingredients combined 1n the stated proportions (111 parts of a 42% solution of iron perchlo- -1 part of a 28% solution of acetic acid,

1 part of a 9% solution of nitric acid, and- 3 ins of chromic acid U. S. P. X. (Cra added tov so composed.

It has been found that it is still possible to obtain results if the proportions of the ingre dientsv of the same concentration are varied within the following limits:

4 to 5 parts of iron perchloride,

1 to 3 parts of acetic acid,

1 to 4 parts of nitric acid, and

3 to 6 grains of chromic acid U. S. P. X. (Croa) to the quart of the mixture.

This solution may be flowed on the late in any known and approved manner, su as,

Y runs toward the sides of each quart of the mixtureV for example, by tiltin the plate in alternate directions, or by whir it to distribute the solution evenly over the surface thereof by centrifugal force. The condition of the plate at this point is clearly shown in Fig. 3, the layer comprising my composition being indicated-atA.

The solution has no effect upon the portions of the surface of theplate which are covered with the resist material, but attacks the .exposed surfaces or bottoms of the plate to a'limited extent, forming a film of corrosion thereon which is readily soluble in the subsequent etching baths. After the solution is flowed on the plate, the vplate is dried and then powdered with the dragons blood or other resist forming material, which is banked against the raised portions ofthe plate, as shown in Fig. 4, with very little attention given to the bottoms or etched portions. l

The plate is next burned in, whereby the previous resist layer of ink and powder is fused on the top and sides of the relief portions with the newly applied layer of powder. As indicated in Fig. 5a, the fused resist pow der forms a layer on top of the dried layer A whichY is composed of my herein described composition together with the corrosion caused by the solution attacking the metal of the plate.

It is to be noted at this point that before flowing my solution over the etched surface of the plate, it has been thoroughly wetted With water during the rinsing process, and due to capillary attraction this aqueous film the raised portions of the plate and lodging therein, serves to dilute the solution of my composition at these points, (designated A in Fig. 4) This phenomenon, together with other effects which will also be described, lessens the corroding effect of my solution on the sides of the lines,.surfaces or dots comprising the raised lportions of the plate and permits the applic resist to adhere to the sides and thus prevent undercutting by the subsequently ein loyed etching solutions.

e e'ect of the solution in preventing the adhering of the resist powder on the sides of the raised portions is also minimized or prevented by the fact that gases which are generated by the action of my solution on the plate do not pass through the central portions of the film between the lines or dots, but up along the sides, thus causingfthe film of corrosion at these points to be of a weaker and more porous nature. These natural tendencies of my'solution to make greater deposits on the bottoms of the plate than at the sides of the lines or dots have the effect of reducing the interference' with the adhering properties of the powdered resist at these points where the latter is banked very heavily during their application by four-way iso vlli

-tops of the plate fuses together with thev resist powder applied to the sides, and causes' the new and augmented resist layer to extend overv the edges and down the sides of the raised portions of the plate'.

Then the. plate is. mmersed again in the etching bath, whereupon the film ofcorrosion producedby my novel solution on the exposed areas is immediately dissolved-re-` leasing from the plate the particlies of drag-A ons blood which adhered to the during the powdering process. In this way, the etching bath durlng this and/ subsequent bites has a perfectly clean bottom to act upon,and this without 'the usualtedious brushing of the powder as in the ordinary process. Furthermore, there exists no necessity for removing the protective composition and the applied resistlayer from the boti toms by mechanical means such as brushing, etc., the entire film of corrosion and resist being'removed automatically in the followinv etching bath.

bue to the obtaining of' such clean bottoms by means of the use of my composi-v tion, there is accomplished not only a great saving due to the ellmination or shortening of the tedious brushing land routing processes, but it is possible to obtain the ordinary four bite depth in but three bites.

In the pursuit of my improved method, it will also be noticed how evenly and clearly all parts of the surface of theplate to be etched open up ;-half tones opening up for 'p the second bite, whereas under the old methods, only the high lights open at this point. The fact that this solution keeps the plate open for later bites is important also in that there is thus eliminated the necessity for trying for excessive depth, as is now done, with a consequent loss of color and fine detail.

It is possible with .the use of my solution .as described herein, to etch any known type of plate or flat, o f whatever siZe,--whethell of fine lines, coarse lines, half tones, crayon work, Ben Day prints or any other kind of work, either alone or miXed,-With ease and without the performance of special operations such as routing or the like.

vIt will be understood that the process and composition which have just been described are susceptible of such modification or variation as is comprised within the scope of the present invention as defined in the subjoined claims. Y

Having thus described the invention, what is claimed as new and desired to be se'cured by Letters Patent is:

1. The process of etching a printing plate a material to said plate after t e initial etching to prevent a subsequently applied 'resist composition from'adherin to thoselportions of'said plate which are tofurther etched,

said material also 'being adapted to lbe removed during such subsequent etching.

2. The rocess of etching printing plates or flats, w ich includes the ste s of applying a resist to portions ofthe' s ace of a-plate, sub'ectingl the plate to an initial immersion in t e etc ing bath and'treating the plate so that the'subsequently applied resist composition may adhere to those portions of said 'plate which are to be further etched duringlsubsequent manipulative processes, ut will be readily dislodged during such subsequent etching.

3. The process of etching printigg plates or flats, which includes the steps with.V a solution having the property of forming a protective film which renders' subsequently applied resist composition non-admg a resist to portions of thesurface of a plate, subjecting the late tov an initial im-V mersion in the etching ath, flowing the plate asv herent, the film vand the resist composition both being adapted to be removed during a subsequent etching step.

4. The process of etching printing. plates Y or ats,.which includes the steps of applying a resist to portions of the surface of said plate, subjecting the plate to an initial immersion in the etching bath, iowing the plate with asolution having' the propert of form. ing a protective layer which ren ers subsequently applied resist compositlon non-adherent durin further etching, powdering the surface o -said plate,.burning in the l`ate and again subjectingit to an immersion m' the etchmg bath.

5. The process set forth in claim plied to a zincplate.

6. The process set forth in claim 2 in whlch the plate is of zinc and an etching bath of nitric acid is used. 7. The process of etching a printin` or fiat whichincludes thesteps of said plate with a solution containing an iron chloride and acetic, nitric, and chromic acids, whereby a subsequently applied resistcomposition is rendered non-adherent to the surfaces to be etched. I

8. The process of etching zinc printing plates which includes thesteps of applying a resist to portions of such av plate, subjecting the plate to an initial immersion in a nitric acid etching bath, flowing said plate with a solution containin iron perchloride, acetic acid, nitric aci and chromic acid,

powdering said plate with a resist composil tion, heating said plate and again subjecting it to an immersion in the etching bath, whereupon the coating of resistvcomposition will be dislodged from the portions to be etched. 9. The photo-engraving process which ,comprises the following steps:-applying a resist composition comprising a suitableink 4 imams and to pin owder, to a develo d plate; subjecting is plate to a'n initial pniimersion in an etc ing bath; rinsing said late with water; flowing the late with a so ution containing iron perch oride, acetic acid, nitric acid, and chromic acid; drying the plate; powdering said plate with dragons blood;

burning 1n the plate; and thereafter alternately etching an powdering the plate until 1o the plate is suiciently engraved.

10. The process-of en raving zinc rinting plates, which includes t e steps of su jecting the plate to an initial etching in a nitric acid bath; rinsing with water; flowing with a solution containing iron perchloride, acetic acid, nitric acid, and chromic acid; drying the plate; brushing with powdered dragons blood; burning in the plate; and subject-- ing the plate to subsequent etching.

11. The process of etching printing plates or the like which includes the steps of treating the plate with a composition which is adapted to form a film of corrosion over the portions of the surface of the plate which is tobe etched; powdering the entire surface of the plate with a resist material; and subsequent y sub`ectinI said plate to an immersion in the etc ing ath, whereupon said film Vis dissolved, carrying away with it the coating of resist material thus ensuring a clean bottom for the etched surface.

12. A composition of matter for use in photoengraving processes comprising iron perchloride, acetic acid, nitric acid, and

chromic acid.

13. A composition of matter for use in photoengraving processes comprising 4 yp adrts of a 42% solution of iron perchlor1 e,

4o 1 part of a 28% solution of acetic acid,

1 part of a 9% solution of nitric acid, and 3 grains of chromic acid U. S. P. X.

(CrOa) added to each quart of the mixture so composed. 14. A composition of matter for use in hotoengraving processes which is prepared y adding from 3 to 6 grains of chromic acid U.- S. P. X. (CrOa) to each quart of a mixture having the following composition 5c 4 to 5 parts of a 42% solution of iron perchloride, l 1 to:1 parts of a 28% solution of acetic acid,

1 to 4 parts of a 9% solution of nitric acid. In testimony whereof I hereunto ax my signature.

MARCUS F. CONROY. 

